A fog generator for a security application is normally technically based on the principle of vaporizing glycol (the fog liquid). Whereby the vaporized fog liquid is emitted into the “area to be fogged” via an outlet channel and a nozzle and there to immediately condense into a dispersed aerosol-like fog under atmospheric pressure and room temperature. This fog takes away the criminal's sight and disorients the criminal.
Increasing the temperature of the fog liquid from room to vaporizing temperature requires 0.8 to 1 kJ per ml. (depending on the applied formulation of the fog liquid, among others, the water content). The heat flow to the transfer surfaces of the vaporization channels/passages is mainly provided for via thermal conduction. The inlet of a heat accumulator, also known in the technical field as a heat exchanger, is connected to a fog liquid reservoir, whereby this fog liquid is injected into the inlet of the heat accumulator at the desired time (fog emission) by overpressure. This overpressure can be generated by:
a) a mechanical pump and/or potential elastic energy (tensioned spring against a piston)
b) operating pressure by compressed or liquid (vapour pressure propellant) propellant, and/or operating pressure generated by gas as a result of a chemical reaction or chain reaction.
A heat accumulator in a fog generator for a security application is characterized by:                A component in which heat (joules) is stored by its heat capacity C (eg. steel: ˜0.46 J/° C. per g) and/or possibly latent congelation heat of a phase-transition agent (for example, see the heat accumulator described in EP2259004)        The temperature of the heat accumulator, at least at the outlet, is higher than the boiling point of the fog liquid to be vaporized.        Heating the heat accumulator to the desired temperature regularly happens via Joules transfer from within an electrical resistance wire.        The transfer of Joules happens intensively between the internal channels and/or free passages of the heat accumulator and the fog liquid flowing through.        All the evaporated fog liquid is emitted into the “area to be fogged” via an outlet channel and a nozzle and to immediately condense into a dispersed aerosol-like fog under atmospheric pressure and room temperature.        
The fog generation capacity (debit ml/sec) of a heat accumulator strongly depends on the fog liquid supply pressure offered at its inlet and its design. In prior art fog generators, the heat accumulator is provided with a channel or a few channels that is/are kept at high temperature (FIG. 1). The fog liquid is vaporized by driving it through the hot channel. The speed of the fog formation is naturally crucial for fog generators for security applications. The current innovations in the field are then also directed at accelerating the speed at which fog is generated (both the speed of the commencement of fog formation and the volume of fog emitted per second). So, for instance, a fog generator is represented in PCT/EP2013/078112, in which a fog liquid is ejected by means of the gas generation out of a pyrotechnic substance. The fog liquid can also be driven out by a compressed/liquid propellant under high pressure (eg. 80 bar). However, it has been established that prior art heat accumulators do not work work optimally for such an, as it were explosive, forcing in of the fog liquid. Because the debit in fog liquid is quickly 10× larger than in current devices, such heat accumulators cannot completely vaporize the liquid, mostly because of insufficient optimally transferable Joules being available at the heat transfer surface during the time that the fog liquid flows through. Consequently, not only gas but also fog liquid is expelled via the exit.
PCT/EP2013/078112 offers a solution thereto by offering a plate heat accumulator with labyrinth-design (FIG. 2), this development facilitates quick heat transfer but also forms a relatively large dynamic resistant (due to the relatively long route to be covered by the liquid to be vaporized). A pressure drop between the inlet and the outlet of the heat accumulator of 50 bar is to be expected in case of a debit of 100 ml fog liquid per second. Although this pressure drop is not that problematic, because of the initial high pressure (80 bar and higher), this heat accumulator has a few further disadvantages. For example, the heat accumulator is cumbersome to produce. The plates have to be pre-formed and welded to each other individually.
However, warping of the plates due to the addition of small distortions during and after the post-shrinking of the welded components showed to be an even greater problem. The sum of all the undesirable distortions is difficult to keep under control even under an axial press, this, due to the quick transition from hot to cold of the plates installed first in respect of the inlet when the liquid is injected, leads to unpredictable clicking. Moreover, it is costly and difficult to design the heat accumulator in a corrosion-resistant manner. Especially this is really important for a heat accumulator in a fog generator, in view of the high temperatures and the oxygen entering from the atmospheric environment (normally entering from the nozzle or as a result of the available oxygen from the thermal end reaction), resulting in the “corrosive” acidity level of the thermal degradation products of the liquids used.
Consequently, there is a need for a heat accumulator for a fog generator that can completely vaporize a large debit of fog liquid and that is resistant to a high operating pressure, simple to produce at a low cost and that can be properly designed corrosion-resistant.